In recent years, interest in using microwave signals for applications in many industrial and medical settings has grown dramatically. One such setting is the sterilizing of medical instruments and other objects. Many devices employ microwaves for steam sterilization. For example, U.S. Pat. No. 4,861,956 describes a "Microwave/steam sterilizer" in which microwaves are used to heat water vapor which in turn heats the objects to be sterilized. In other devices, the object to be sterilized is microwave heated together with a liquid that vaporizes during heating. U.S. Pat. No. 5,039,495 describes such a device. In the disclosed device, objects are placed in a microwave-permeable pouch together with a liquid and the arrangement is exposed to microwave energy.
Although many microwave/steam sterilizers are in use, the prior art has only partially explored adapting the shapes of microwave structures to maximize the efficiency of heating liquids. U.S. Pat. No. 4,400,357 discloses a narrow receptacle for enhanced vaporizing of a liquid in the context of a sterilization device. That patent also discloses use of bifocal radiation to enhance heating of a liquid. However, that patent does not disclose locating receptacles at electromagnetic field peaks. That patent also does not disclose a pointed receptacle base for creating a region of increased field intensity near the liquid.
Efficient heating of liquids is particularly important in the context of autoclaves which rely on higher pressures for enhanced sterilizing. At higher pressures, liquids must be heated to higher temperatures in order to create vapor. Thus, high-pressure sterilizers would particularly benefit from increased efficiency in liquid heating.
Another context in which efficient heating of liquids is particularly important is in the context of steaming vegetables and other foods. When steaming vegetables in a microwave, it is desirable for the steam, rather than the microwave energy, to cook the vegetables. As a result, it is important to boil the water rapidly so that the vegetables are steamed quickly, before overexposure to microwaves gives them an rubbery texture. Although microwave steamers exist in the marketplace today, they are not designed optimally to expose the water to regions of peak field intensity.